Photoreactive adhesive composition and method of bonding with the same

ABSTRACT

A photoreactive adhesive composition which is of the one-pack type, has excellent workability, cures upon irradiation with light, and can have sufficient initial adhesion strength and heat resistance immediately after bonding. The photoreactive adhesive composition comprises a urethane prepolymer and a compound which generates an amine upon irradiation with light, wherein the amine-generating compound is a cobalt/amine complex, O-acyloxime, or carbamic acid derivative.

TECHNICAL FIELD

[0001] This invention relates to a one-part photoreactive adhesivecomposition and a joining method utilizing the same, and moreparticularly to a photoreactive adhesive composition which exhibitssufficient initial bond strength and heat resistance via a reaction ofan isocyanate group with an amino group produced when it is exposed to alight, and a joining method utilizing the same.

BACKGROUND ART

[0002] A one-part adhesive is generally supplied in the liquid form andcoated onto an adherend, as by a brush or roller, which is subsequentlyjoined to another adherend. After the joining, the adhesive solidifiesas a result of evaporation of a solvent or growth of its molecularweight, so that the adherends are firmly bonded to each other.

[0003] General liquid adhesives exhibit high bond strength aftercompletion of curing but need a relatively long time to complete thereaction. Accordingly, adherends must be provisionally held in contactwith each other in some way until the liquid adhesive solidifies. Thisresults in the insufficient workability.

[0004] Solvent-borne adhesives need a drying oven to vaporize a solventand adversely affect working environments, which has been a problem.

[0005] As a solution to the above-described problems, Japanese PatentLaying-Open No. Sho 61-31418 discloses a one-part urethane adhesive. Theone-part urethane adhesive exhibits high bond strength because it curesby a moisture-curing reaction. However, the one-part urethane adhesivefails to provide sufficient initial bond strength since itsmoisture-curing reaction proceeds insufficiently just after it hascombined adherends together, and exhibits insufficient heat resistancejust after it has combined adherends together.

[0006] Japanese Patent Laying-Open No. Sho 64-24821 discloses aphotocurable polyurethane composition which contains a polyurethaneoligomer having an active isocyanate group, a UV-curable organiccompound having a hydroxyl group, and a photoinitiator.

[0007] Japanese Patent Publication No. Hei 7-103356 discloses a bondingmethod utilizing a photocurable polyurethane composition which containsan isocyanate compound, a free-radically photopolymerizable compound anda free-radically photopolymerizable monomer.

[0008] In cases where the preceding photocurable polyurethanecompositions utilizing a free-radical photopolymerization reaction areused as adhesives, photocurable components must be increased in contentsand crosslinked by irradiation to improve heat resistance of theadhesives immediately after combination of adherends. However, when thephotocurable components are increased in contents and crosslinked byirradiation, adhesion of the composition to the adherends is lowered toresult in the problematic reduction in initial bond strength and bondstrength after cure.

DISCLOSURE OF THE INVENTION

[0009] It is an object of the present invention to provide aphotoreactive adhesive composition which overcomes the above-describeddeficiencies encountered in prior art, is of the one-part type, hasexcellent workability, cures upon exposure to a radiation, and exhibitssufficient initial bond strength and heat resistance immediately afterit has combined adherends.

[0010] The photoreactive adhesive composition in accordance with thepresent invention is characterized as containing A: an urethaneprepolymer and B: a compound which generates amine upon exposure to aradiation, as essential components.

[0011] Preferably, a compound represented by the following formula 1, 2or 3 is used as the aforementioned compound B.

[0012] In the formula 1, R1 is a main chain of a high polymer which has,at its side or end, an n-valent hydrocarbon or aromatic group, or ngroups represented by the formula 1a, and n is an integer of 1 orlarger.

[0013] In the formulas 1 and 1a, R1a is an aromatic or alkyl group andR1b is an aromatic or alkyl group.

[0014] In the formula 2, R2 is a functional group comprised of C and Hor C, H and O, preferably a hydrocarbon or aromatic group, morepreferably an alkyl or alkylene group or a group represented by thefollowing formula 2x, R3 and R4 represent any of hydrogen, halogen andalkyl, R5-R9 represent any of hydrogen, halogen, alkyl, alkoxy andnitro, and n is an integer of 1 or larger.

[0015] In the formula 2x, R is an organic group, preferably an alkylenegroup.

[0016] In the formula 3, R10 is a functional group comprised of C and Hor C, H and O, preferably a hydrocarbon or aromatic group, morepreferably an alkyl or alkylene group or a group represented by thefollowing formula 3x, R11 is hydrogen, halogen or alkyl, R5-R9 representany of hydrogen, halogen, alkyl, alkoxy and nitro, and n is an integerof 1 or larger.

[0017] In the formula 3x, R is an organic group, preferably an alkylenegroup, more preferably a methylene or ethylene group.

[0018] (Urethane Prepolymer)

[0019] The urethane prepolymer is obtained as a reaction product of apolyhydroxy compound and a polyisocyanate compound and has an isocyanateresidue.

[0020] The polyhydroxy compound for use in the preparation of theurethane prepolymer is not particularly specified in type. Examples ofpolyhydroxy compounds include those generally used in the preparation ofurethane compounds, such as polyether polyol, polyester polyol andpolymer polyol.

[0021] The above-listed polyhydroxy compounds may be used alone or incombination.

[0022] The polyether polyol is not particularly specified and may be apolymer obtained, for example, by allowing alkylene oxide to undergo aring-opening polymerization under the presence of a low-molecular,active hydrogen compound having at least two active hydrogens.

[0023] Specific examples of low-molecular, active hydrogen compoundshaving at least two active hydrogens include diols such as bisphenol A,ethylene glycol, propylene glycol, butylene glycol and 1,6-hexane diol;triols such as glycerin and trimethylolpropane; and amines such asethylenediamine and butylenediamine.

[0024] These low-molecular, active hydrogen compounds having at leasttwo active hydrogens may be used alone or in combination.

[0025] Specific examples of alkylene oxides include, but not limited to,ethylene oxide, propylene oxide, butylene oxide, amylene oxide, hexyleneoxide, and tetrahydrofuran.

[0026] The above-listed alkylene oxides may be used alone or incombination.

[0027] Example of polyester polyols include, but not limited to,polymers obtained via dehydration condensation of a polybasic acid, suchas adipic acid, azelaic acid, sebacic acid, terephthalic acid,isophthalic acid or succinic acid, with a polyol such as bisphenol A,ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, diethyleneglycol, 1,6-hexane glycol or neopentyl glycol; polymers of lactones suchas ε-caprolactone and α-methyl-ε-caprolactone; and polymers obtained bydehydration condensation of a hydroxycarboxylic acid, such as castor oilor a reaction product of castor oil and ethylene glycol, with any of theabove-listed polyols.

[0028] The above-listed polyester polyols may be used alone or incombination.

[0029] The polymer polyol is not particularly specified in type.Examples of polymer polyols include graft polymers obtained via graftcopolymerization of an ethylenically unsaturated compound, such asacrylonitrile, styrene or methyl (meth)acrylate, with any of theabove-listed polyether polyols and polyester polyols; 1,2-polybutadienepolyol, 1,4-polybutadiene polyol and hydrides thereof.

[0030] The above-listed polymer polyols may be used alone or incombination.

[0031] Although not particularly limiting, the polymer polyol preferablyhas a weight average molecular weight in the approximate range of100-50,000, more preferably in the approximate range of 500-5,000.

[0032] Examples of polyisocyanate compounds useful in the preparation ofthe urethane prepolymer include, but not specifially limited to,2,4-tolylene diisocyanate, phenylene diisocyanate, xylene diisocyanate,4,4′-diphenylmethane diisocyanate (MDI), a mixture (crude MDI) of MDIwith triphenylmethane triisocyanate or the like, 1,5-naphthylenediisocyanate, isophorone diisocyanate, dicyclo-hexylmethanediisocyanate, ethylene diisocyanate, methylene diisocyanate, propylenediisocyanate, tetramethylene diisocyanate, triphenylmethanetriisocyanate and hydrides thereof. The use of MDI and crude MDI, amongthem, is preferred for their excellence in safety and reactivity.

[0033] The above-listed polyisocyanates may be used alone or incombination.

[0034] A preparation method of the urethane prepolymer is notparticularly specified. For example, the aforementioned polyhydroxycompound and polyisocyanate compound may be mixed such that a ratio inequivalents of the isocyanate (NCO) group of the polyisocyanate compoundto the hydroxyl (OH) group of the polyhydroxy compound, i.e., an NCO/OHequivalent ratio falls within the range of 1.2-15, preferably 3-12. Thesubsequent reaction of the mixture at about 80-100° C. for about 3-5hours, under a nitrogen stream, results in obtaining the urethaneprepolymer.

[0035] If the NCO/OH equivalent ratio falls below 1.2, a viscosity of aresulting urethane prepolymer may become excessively high to result inthe difficulty to prepare an adhesive composition. On the other hand, ifthe NCO/OH ratio exceeds 15, a resulting adhesive composition increasesits tendency to foam when it is cured and may in some cases lower acohesion of a cured product to result in the failure to exhibitsufficient bond strength.

[0036] (Compound Which Generates Amine upon Exposure to Radiation)

[0037] The compound which generates amine upon exposure to radiation,for use in the present invention, is not particularly specified, so longas it has the ability to generate amine upon exposure to radiation.Useful compounds preferably generate polyfunctional amine, morepreferably primary or secondary amine having plural amino groups.

[0038] Examples of such compounds include (1) a cobalt amine complex,(2) O-acyloxime and (3) carbamic acid derivative, which are all belowdescribed.

[0039] (1) Cobalt amine complex: Co(NH₂R12)₅X²⁺

[0040] wherein R12 represents H or CH₃ and X represents halogen.

[0041] (2) The compound represented by the formula 1 is used as theO-acyloxime. In the formula 1, R1 represents a main chain of a highpolymer which has, at its side or end, n-valent hydrocarbon or aromaticgroup or n groups represented by the formula 1a, and n is an integer of1 or larger. Preferably, R1 is an alkyl, aromatic, alkylene, a mainchain of an olefinic polymer, or an ethylenically unsaturated functionalgroup. More preferably, R1 is a compound represented by any of thefollowing formulas 5a-5b.

[0042] (3) Carbamic acid derivative

[0043] Examples of carbamic acid derivatives include the compoundsrepresented by the formulas 2 and 3. In the formulas 2 and 3, R2 is afunctional group comprised of C and H, or C, H and O, specific examplesof which include alkyl and aromatic groups.

[0044] In the formula 2, the following a)-c) illustrate suitablecombinations of the substituent groups R3-R9.

[0045] a) At least one of R5 and R9 is a nitro group, R6-R8 areindependently hydrogen or methoxy, and R3 and R4 are independentlyhydrogen or alkyl having 1-2 carbon atoms.

[0046] b) R7 is a nitro group, R5, R6, R8 and R9 are independentlyhydrogen or methoxy, and R3 and R4 are independently hydrogen or alkylhaving 1-2 carbon atoms.

[0047] c) R6 and R8 are both methoxy, R5, R7 and R9 are all hydrogen,and R3 and R4 are independently hydrogen or alkyl having 1-2 carbonatoms.

[0048] One preferred method for synthesis of the compound represented bythe formula 2 involves reacting 2-nitrobenzyl alcohol or its derivativewith a polyfunctional isocyanate compound.

[0049] Examples of useful polyfunctional isocyanate compounds include,but not limited to, 2,4-tolylene diisocyanate (TDI), 2,6-tolylenediisocyanate (TDI), 1,3-bis(isocyanatomethyl)benzene (XDI),1,3-bis(isocyanatomethyl)cyclohexane (H6XDI), hexamethylene diisocyanate(HDI), phenylene diisocyanate, xylene diisocyanate, 4,4′-diphenylmethanediisocyanate (MDI), a mixture (crude MDI) of MDI and triphenylmethanetriisocyanate or the like, 1,5-naphthylene diisocyanate, isophoronediisocyanate, dicyclohexylmethane diisocyanate, ethylene diisocyanate,methylene diisocyanate, propylene diisocyanate, tetramethylenediisocyanate, triphenylmethane triisocyanate, and their hydrides.

[0050] In the synthesis of the compound represented by the formula 2, acatalyst known as being useful in reacting hydroxyl with isocyanategroups, e.g., a metal acetate, metal chloride, copper sulfate ordi-n-butyltin dilaurate, may be used.

[0051] The compounds represented by the following formulas 2a-2c maypreferably be useful as the compound represented by the formula 2.

[0052] Synthesis of the compound represented by the formula 3 may beachieved by utilizing a reaction between amine and organic acid orbetween isocyanate and organic acid, for example.

[0053] For example, a) a reaction of diphenylmethane-4,4′-diamine withaliphatic acid, benzoic acid or the like, or alternatively, b) areaction of diphenylmethane-4,4′-diisocyanate with aliphatic acid,benzoic acid or the like may be utilized to synthesize the compoundrepresented by the formula 3.

[0054] In the synthesis of the compound represented by the formula 3, acatalyst known as being useful in reacting amino with carboxyl groups orisocyanate with carboxyl groups may also be used.

[0055] The compounds represented by the following formulas 3a-3e maypreferably be useful as the compound represented by the formula 3. Inthe formulas 3a-3c, R11 and R13 represent any of hydrogen, hydrocarbonand aromatic groups, and R12 is a divalent organic group, preferably adivalent hydrocarbon group, more preferably an alkylene group.

[0056] (Blending Proportion)

[0057] In the present invention, the urethane prepolymer and thecompound which generates amine upon exposure to radiation may preferablybe blended such that a ratio of equivalents of the isocyanate group ofthe urethane prepolymer to the amino group to be generated upon exposureto radiation falls within the range of 1:0.01-1:1.2. If the equivalentof the amino group, based on 1 equivalent of the isocyanate group, isbelow 0.01, curing of the urethane prepolymer when exposed to radiationmay become insufficient to result in the failure to exhibit sufficientinitial bond strength and heat resistance. If it exceeds 1.2, theexposure of the adhesive composition to radiation may result in thereduced adhesion between adherends, the shortened work life and theinsufficient bond strength.

[0058] (Photosensitizer)

[0059] When necessary, a photosensitizer may be further added to thephotoreactive adhesive composition in accordance with the presentinvention. Useful photosensitizers include triplet excitation energytransfer photosensitizers and electron transfer photosensitizers.Specific examples of photosensitizers include acetophenones,benzophenone, Michler's ketone, benzil, benzoin, benzoin ether,benzyldimethyl ketal, benzoyl benzoate, α-acyloxime ester,tetramethylthiuram monosulfide, thioxanthone and its derivatives,aliphatic amine, aromatic-containing amine, aromatic compounds with anitrogen atom constituting a part of an aromatic ring such aspiperidine, allylthiourea, O-tolylthiourea, sodium diethyldithiophosphate, soluble salts of aromatic sulfinic acid,N,N-disubstituted-p-aminobenzo-nitrile compounds, tri-n-butylphosphine,N-nitrosohydroxyl-amine derivatives, oxazolidine compounds,tetrahydro-1,3-oxazine compounds, formaldehyde and its condensate withdiamine, anthracene and its derivatives, xanthine; cyanine dyes such asphthalocyanine, naphthocyanine and thiocyanine; and porphyrin and itsderivatives.

[0060] Among them, thioxanthone and its derivatives, as represented bythe following formula 4, are preferred for their superior ability toincrease the radiation sensitivity of the compound B.

[0061] In the formula, R4a is hydrogen, alkyl or halogen and R4b ishydrogen or alkyl. Preferably, R4a is Cl and R4b is H, R4a and R4b areboth ethyl, R4a and R4b are both isopropyl, or R4a and R4b are bothmethyl.

[0062] (Gel Fraction After Irradiation)

[0063] Preferably, the photoreactive adhesive composition in accordancewith the present invention, immediately after its exposure to radiation,exhibits a gel fraction in the range of 5 weight %-60 weight %, morepreferably in the range of 10-50 weight %. This assures sufficient heatresistance of the adhesive composition immediately after irradiation.When necessary, subsequent to irradiation, heat may be applied toaccelerate a curing reaction of the composition and increase its heatresistance just after irradiation.

[0064] (Additives)

[0065] Other than the essential components, the adhesive composition inaccordance with the present invention may further contain, within therange that does not interfere with the purposes of the presentinvention, one or more of the following additives: a silane couplingagent as an adhesion-imparting agent; filler; thixotropic agent;colorant; plasticizer (softener); stabilizer; antioxidant; UV absorber;and organic solvent.

[0066] Examples of silane coupling agents include, but not limited to,aminoalkoxy silanes such as γ-aminomethyl-triethoxysilane andN-β(aminoethyl)-γ-aminopropyltrimethoxy-silane; mercaptoalkoxy silanessuch as γ-mercaptopropyl-trimethoxysilane; epoxyalkoxy silanes such asγ-glycidoxy-propyltrimethoxysilane and3,4-epoxycyclohexylethyl-trimethoxysilane; vinyl silanes such asvinyl-tris(β-methoxyethoxy)silane and vinyltriethoxysilane; and silanecompounds having isocyanate and alkoxysilyl groups, one for each, suchas γ-isocyanatepropyltriethoxysilane. One or more of these silanecoupling agents may be suitably used.

[0067] Examples of fillers include, but not particularly limited to,mica powder, calcium carbonate, surface-treated calcium carbonate,carbon blck, talc, titanium oxide, rubber powder, organic balloon,inorganic balloon and wollastonite. One or more of these fillers may besuitably used.

[0068] The filler is not particularly specified in shape and may haveany form of a powder, flake, sphere, bulk and needle.

[0069] Examples of thixotropic agents include, but not limited to,colloidal silica, hydrogenated castor oil and organic bentonite. One ormore of these may be suitably used.

[0070] Examples of plasticizers include, but not limited to, dioctylphthalate (DOP), dibutyl phthalate, dilauryl phthalate, dioctyl adipate,diisodecyl adipate, tributyl phosphate, trioctyl phosphate, propyleneadipate glycol polyester, butylene adipate glycol polyester, epoxidizedis soybean oil, chlorinated paraffin and liquid paraffin. One or more ofthese may be suitably used.

[0071] Examples of stabilizers include, but not limited to, “TINUVIN327” (product of Ciba Geigy Co.), “IRGANOX 1010” (product of Ciba GeigyCo.) and “TOMISORP 800” (product of Yoshitomi Pharmaceutical Indstries,Ltd.). One or more of these may be suitably used.

[0072] Examples of organic solvents include, but not limited to,synthetic isoparaffin solvents having flash points of 40° C. and higher.One or more of these may be suitably used.

[0073] The photoreactive adhesive composition in accordance with thepresent invention is used in the form of a one-part urethane-basedphotoreactive adhesive, as described above. When exposed to a radiation,the above-specified compound generates amine which is subsequentlycaused to react with the isocyanate group of the urethane prepolymer.

[0074] Because this reaction proceeds quickly, the compositionimmediately after it combines adherends exhibits sufficient initialtack, holding power and heat resistance The curing reaction of theurethane prepolymer is subsequently allowed to proceed with the aid of amoisture. As a result, the composition finally exhibits high bondstrength.

[0075] In addition to being useful as an adhesive, the photoreactiveadhesive composition in accordance with the present invention is usefulas a sealer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0076]FIG. 1 is a chart showing an infrared absorption spectrum of thecompound 1 prepared in the Example;

[0077]FIG. 2 is a chart showing an infrared absorption spectrum of thecompound 2 prepared in the Example;

[0078]FIG. 3 is a chart showing an infrared absorption spectrum of thecompound 3 prepared in the Example; and

[0079]FIG. 4 is a chart showing an infrared absorption spectrum of thecompound 4 prepared in the Example.

BEST MODE FOR CARRYING OUT THE INVENTION

[0080] The following non-limiting examples illustrate the presentinvention.

[0081] (Synthesis of the Compound Represented by the Formula 1)

[0082] Compound 1

[0083] 2.7 g of the acetophenone oxime represented by the followingformula 6 was dissolved in 5 ml chloroform to which 1.55 g of thesuccinyl chloride represented by the following formula 7 wassubsequently added in a dropwise manner. Thereafter, the mixture wasstirred at room temperature for 24 hours. The resulting white solid wasdissolved in chloroform and then recrystalized. The resulting crystalwas designated as the compound 1 having the structure specified by thepreceding formula 5a.

[0084] (Synthesis of the Compound Represented by the Formula 2)

[0085] Compound 2

[0086] 2-nitrobenzyl alcohol was dissolved in methyl ethyl ketone (MEK)to which 2,4-tolylene diisocyanate (TDI) was added dropwise such that aratio in moles of the OH group of 2-nitrobenzyl alcohol to the NCO groupof TDI was brought to 1:1. Thereafter, they were allowed to react untilthe isocyanate group was reduced to 10% or less of its initial amount.

[0087] The resulting white crystal was washed with MEK to removeresidual 2-nitrobenzyl alcohol and TDI that were left unreacted, andthen designated as the compound 2 having the structure specified by thefollowing formula 8.

[0088] Compound 3

[0089] 2-nitrobenzyl alcohol was dissolved in methyl ethyl ketone (MEK)to which hexamethylene diisocyanate (HDI) was added dropwise such that aratio in moles of the OH group of 2-nitrobenzyl alcohol to the NCO groupof HDI was brought to 1:1. Thereafter, they were allowed to react untilthe isocyanate group was reduced to 10% or less of its initial amount.

[0090] The resulting white crystal was washed with MEK to removeresidual 2-nitrobenzyl alcohol and HDI that were left unreacted, andthen designated as the compound 3 having the structure specified by thefollowing formula 9.

[0091] (Synthesis of the Compound Represented by the Formula 4)

[0092] Compound 4

[0093] 4,4′-diphenylmethane diisocyanate (MDI) was dissolved in MEK towhich formic acid was added dropwise such that a ratio in moles of theCOOH group of formic acid to the isocyanate group of MDI was brought to1:1. Thereafter, they were allowed to react until the isocyanate groupwas reduced to 10% or less of its initial amount.

[0094] The resulting white crystal was washed with MEK to removeresidual formic acid and MDI that were left unreacted, and thendesignated as the compound 4 having the structure specified by thefollowing formula 10.

[0095] (Structure Identification of the Compound 1-4 from InfraredAbsorption Spectra)

[0096] FIGS. 1-4 are charts respectively showing infrared absorptionspectra of the compounds 1-4. Characteristic frequencies appearing onthe respective charts for the compounds 1-4 and their correspondingbonds are listed in the following Table 1. TABLE 1 Compound 1

Compound 2

Compound 3

Compound 4

[0097] (Preparation of Urethane Prepolymer)

[0098] A polyol was provided containing 50 parts by weight of polyethertriol having a number average molecular weight of 4,000 (product ofAsahi Denka Kogyo Co., proudct name: ADEKA POLYETHER T-4000) and madevia ring-opening polymerization of trimethylolpropane and propyleneoxide, and 50 parts by weight of polyether polyol (number averagemolecular weight of 6,000) made via ring-opening polymerization ofpropylene oxide. This polyol was blended withdiphenylmethane-4,4′-diisocyanate (product of Nippon PolyurethaneIndustry, Co., Ltd., product name: MILIONATE MT) so that a ratio of theNCO group of the diisocyanate to the OH group of the polyol, i.e., anNCO/OH ratio was brought to 1:1. The blend was subsequently allowed toreact at 80° C. for 5 hours, so that a urethane prepolymer was obtained.

EXAMPLE 1

[0099] 5 parts by weight of the compound 1 was added to 100 parts byweight of the urethane prepolymer. The mixture was stirred undernitrogen atmosphere to homogeneity so that a one-part photoreactiveadhesive composition was obtained.

EXAMPLE 2

[0100] 5 parts by weight of the compound 2 was added to 100 parts byweight of the urethane prepolymer. The mixture was stirred undernitrogen atmosphere to homogeneity so that a one-part photoreactiveadhesive composition was obtained.

EXAMPLE 3

[0101] The procedure of Example 1 was followed, except that the compound2 was replaced by the compound 3, to obtain a one-part photoreactiveadhesive composition.

EXAMPLE 4

[0102] The procedure of Example 1 was followed, except that the compound1 was replaced by the compound 3, to obtain a one-part photoreactiveadhesive composition.

EXAMPLE 5

[0103] 5 parts by weight of the compound 1, together with 0.5 parts byweight of thioxanthone (“DETX-S”, name used in trade and manufactured byNippon Kayaku Co.) as a photosensitizer, were added to 100 parts byweight of the urethane prepolymer. The mixture was stirred undernitrogen atmosphere to homogeneity so that a one-part photoreactiveadhesive composition was obtained.

EXAMPLE 6

[0104] The procedure of Example 5 was followed, except that the compound1 was replaced by the compound 2, to obtain a one-part photoreactiveadhesive composition.

EXAMPLE 7

[0105] The procedure of Example 5 was followed, except that the compound1 was replaced by the compound 3, to obtain a one-part photoreactiveadhesive composition.

EXAMPLE 8

[0106] The procedure of Example 5 was followed, except that the compound1 was replaced by the compound 4, to obtain a one-part photoreactiveadhesive composition.

EXAMPLE 9

[0107] parts by weight of the compound 1, together with 0.5 parts byweight of benzophenone as a photosensitizer, were added to 100 parts byweight of the urethane prepolymer. The mixture was stirred undernitrogen atmosphere to homogeneity so that a one-part photoreactiveadhesive composition was obtained.

COMPARATIVE EXAMPLE

[0108] The urethane prepolymer was used alone.

[0109] (Evaluation)

[0110] The one-part photoreactive adhesive compositions of Examples 1-9and the prepolymer of Comparative Example were evaluated for (1) initialbond strength, (2) bond strength after cure, (3) heat resistance and (4)gel fraction in accordance with the following procedures.

[0111] (1) Initial bond strength: Each adhesive was applied onto onesurface of a stainless steel plate (measuring 3 cm×10 cm×0.2 cm andweighing 45 g) previously polished at 23° C. atmosphere to providethereon a 100 μm thick, 3 cm×3 cm adhesive coat. Thereafter, theadhesive coat was exposed to a radiation at 40 mW/cm² for 10 minutes,using a high-pressure mercury lamp (JETLIGHT-2300 manufactured by OakSeisakusho Co.). Another stainless steel plate, measuring 3 cm×10 cm×0.2cm and weighing 45 g, was placed onto the adhesive coat. Immediatelyafter combination, the laminate was measured for shear bond strength ata pulling rate of 50 mm/min to determine an intial bond strength.

[0112] (2) Bond strength aftre cure: Each adhesive was applied onto onesurface of a stainless steel plate (measuring 3 cm×10 cm×0.2 cm andweighing 45 g) previously polished at 23° C. atmosphere to providethereon a 100 um thick, 3 cm×3 cm adhesive coat. Thereafter, theadhesive coat was exposed to a radiation at 40 mW/cm² for 10 minutes,using a high-pressure mercury lamp (JETLIGHT-2300 manufactured by OakSeisakusho Co.). Another stainless steel plate, measuring 3 cm×10 cm×0.2cm and weighing 45 g, was placed onto the adhesive coat. The laminatewas aged at 23° C. for 7 days and then measured for shear bond strengthat a pulling rate of 50 mm/min to determine a bond strength after cure.

[0113] (3) Heat resistance measurement: Each adhesive was applied onto astainless steel plate previously polished at 23° C. atmosphere toprovide thereon a 100 μm thick adhesive coat which was then exposed to aradiation at 40 mW/cm² for 10 minutes, using a high-pressure mercurylamp (JETLIGHT-2300 manufactured by Oak Seisakusho Co.). Anotherstainless steel plate, measuring 3 cm×10 cm×0.2 cm and weighing 45 g,was placed onto the adhesive coat. Immediately after combination, thetest piece was placed in a 150° C. oven. One of the stainless steelplates was fixed to suspend the test piece in a manner that its adhesivesurface oriented vertically. After the 30-minute observation, thedownward movement of the other stainless steel plate was measured.

[0114] (4) Gel fraction measurement: Each adhesive was applied onto apolyethylene terephthalate film surface that was release treated at 23°C. atmosphere to provide thereon a 100 um thick adhesive coat which wassubsequently exposed to a radiation at 40 mW/cm² for 10 minutes, using ahigh-pressure mercury lamp (JETLIGHT-2300 manufactured by Oak SeisakushoCo.). After removal from the release surface, the adhesive coat wasdissolved in tetrehydrofuran. An insoluble matter was regarded as a gelto determined a gel fraction.

[0115] The results are given in the following Table 2. TABLE 2 InitialBond Bond Strength Gel Strength After Cure Fraction (N/cm²) (N/cm²) HeatResistance (Wt. %) Ex. 1 55 490 No Appreciable 15 Movement Ex. 2 49 490No Appreciable 10 Movement Ex. 3 49 490 No Appreciable 10 Movement Ex. 449 490 No Appreciable 5 Movement Ex. 5 65 490 No Appreciable 20 MovementEx. 6 58 490 No Appreciable 15 Movement Ex. 7 58 490 No Appreciable 15Movement Ex. 8 58 490 No Appreciable 10 Movement Ex. 9 60 490 NoAppreciable 10 Movement Comp. Ex. 0 50 Dropped After 0 30 Sec.

[0116] The adhesive of Comparative Example, because of its soleinclusion of the urethane prepolymer, exhibits little intial bondstrength immediately after it has combined the plates. It also shows alow level of heat resistance.

[0117] On the other hand, the adhesive compositions of Examples 1-9exhibit sufficient initial bond strength and heat resistance since theygenerate amine upon exposure to a radiation and a reaction of thegenerated amine with the isocyanate group proceeds quickly. The adhesivecomposition of Example 5 exhibits the increased initial bond strengthcompared to the adhesive composition of Example 9. This is considereddue to the increased photosensitizing action of thioxanthone thanbenzophenone.

UTILITY IN INDUSTRY

[0118] The photoreactive adhesive composition in accordance with thepresent invention constitutes a one-part adhesive using the urethaneprepolymer. Because of inclusion of the compound which generates amineupon exposure to a radiation, the composition when exposed to aradiation, either before or after combination of adherends, generatesamine with which the isocyanate group of the urethane prepolymer reactsquickly. Accordingly, the composition exhibits sufficient initial bondstrength and heat resistance immediately after it combines theadherends. This eliminates or simplifies a troublesome operation inwhich members are provisionally held together before they are finallyjoined. As a result, a bonding procedure is effectively eased.

[0119] Also, a moisture-curing reaction of the isocyanate group of theurethane prepolymer further proceeds. As a result, the compositionfinally exhibits high bond strength comparable in level to conventionaladhesives using the urethane prepolymer.

[0120] When the compounds represented by the formulas 1-3 are used asthe preceding compound which generates amine upon exposure to aradiation, the composition upon exposure to a radiation generatesprimary or secondary amine with which the isocyanate group presenttherein reacts quickly. As a result, the composition immediately afterit combines adherends exhibits the effectively increased initial bondstrength and heat resistance.

[0121] The method of joining members in accordance with the presentinvention utilizes the photoreactive adhesive composition in accordancewith the the present invention. In the method, the adhesive compositionis exposed to a radiation, either before or after it combines themembers, so that amine is generated to duly react with the isocyanategroup. Hence, the improved initial bond strength and heat resistanceresults. This eliminates or simplifies a troublesome operation, such asprovisional fixing. As a result, a bonding procedure is effectivelyeased. Finally, a moisture-curing of the urethane prepolymer assuresfirm adhesion between the members.

1. A photoreactive adhesive composition characterized as comprising: A.an urethane prepolymer; and B. a compound which generates amine uponexposure to a radiation.
 2. The photoreactive adhesive composition asrecited in claim 1 wherein: said compound B which generates amine uponexposure to a radiation is a compound represented by the followingformula 1

 (In the formula 1, R1 is a main chain of a high polymer which has, atits side or end, an n-valent hydrocarbon or aromatic group or n groupsrepresented by the formula 1a and n is an integer of 1 or larger. In theformulas 1 and 1a, R1a is an aromatic or alkyl group and R1b is anaromatic or alkyl group.)
 3. The photoreactive adhesive composition asrecited in claim 1 wherein: said compound B which generates amine uponexposure to a radiation is a compound represented by the followingformula 2

 wherein R2 is a functional group comprised of C and H or C, H and O, R3and R4 represent any of hydrogen, hologen and alkyl, R5-R9 represent anyof hydrogen, halogen, alkyl, alkoxy and nitro, and n is an integer of 1or larger.
 4. The photoreactive adhesive composition as recited in claim1 wherein: said compound B which generates amine upon exposure to aradiation is a compound represented by the following formula 3

 wherein R10 is a functional group comprised of C and H or C, H and O,R11 represents hydrogen, hydrocarbon or aromatic, and n is an integer of1 or larger.
 5. A photoreactive adhesive composition characterized ascomprising: A. an urethane prepolymer; B. a compound which generatesamine upon exposure to a radiation; and C. a photosensitizer.
 6. 2. Thephotoreactive adhesive composition as recited in claim 5 wherein: saidphotosensitizer is a thioxanthone compound represented by the followingformula 4

 wherein R4a is hydrogen, alkyl or halogen and R4b is hydrogen or alkyl.7. A method of joining members characterized as including the steps ofcombining said members by using the adhesive composition as recited inany one of claims 1-6, and exposing the adhesive composition to aradiation prior to, simultaneously with or subsequent to the combinationof the members.